matrix manipulating

Hi there Peculiar problem to me.

I have a 3x3 matrix

w =

     1     2     3
     4     5     6
     7     8     9

and x =

    1.2000    2.6000

I want to access the values of the matrix at the locations given by 'x'.

So I use

round(x), and get x=(1,3).

The value of the matrix at 'x' is '7'.

Now, I want values in the matrix which are 1 cell adjacent to 'x', including 'x'. So that would be

(1,3), (2,3),(3,3), (1,2),(1,1)

and multiply them all.

and give a single output of the product.

Kindly help, mates!

Thanks

Answer 1

[Walter Roberson]

x at location (1,3) is 3, not 7. x(3,1) is the one which is 7.

Array indexing is row first and then column. Arrays are stored internally in memory by going down columns. The internal order of the array you show would be 1, 4, 7, 2, 5, 8, 3, 6, 9.

Anyhow, I cannot see any way that the positions you list could be considered "adjacent" unless you are wrapping around in both the horizontal and vertical directions.

If you want horizontal and vertical wrapping, then:

Let R be the number of rows and C be the number of columns. Let x be the row number and y the column number for the position to work relative to. Then the positions you want are:

X = 1+mod([x;x-1;x+1;x;x]-1,R);
Y = 1+mod([y,y,y,y-1,y+1]-1,C);